springmvc源码笔记-RequestMappingHandlerMapping

下图是springmvc的执行流程

图片来源：www.jianshu.com/p/8a20c547e…

DispatcherServlet根据url定位到Controller和方法，依赖的是HandlerMapping接口的各个实现类，其中，RequestMappingHandlerMapping是专门用来处理注解方式的Controller的

下面，我们分RequestMappingHandlerMapping的加载以及RequestMappingHandlerMapping如何根据url定位Controller两部分来讲

RequestMappingHandlerMapping加载过程

1. RMHP在系统启动时会被注册成bean，见《springmvc源码笔记-HandlerMapping注入》

2. 因为RMHP实现了InitializingBean接口，在bean加载完成后会自动调用afterPropertiesSet方法，在此方法中调用了AbstractHandlerMethodMapping#initHandlerMethods()来实现初始化

   protected void initHandlerMethods() {
   	// 遍历所有的bean
   	for (String beanName : getCandidateBeanNames()) {
   		if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
   			processCandidateBean(beanName);
   		}
   	}
   	handlerMethodsInitialized(getHandlerMethods());
   }
   
   protected void processCandidateBean(String beanName) {
   	Class<?> beanType = null;
   	try {
   		beanType = obtainApplicationContext().getType(beanName);
   	}
   	......
   	// isHandler判断类是否有Controller或者RequestMapping注解
   	if (beanType != null && isHandler(beanType)) {
   		detectHandlerMethods(beanName);
   	}
   }
   
   protected void detectHandlerMethods(Object handler) {
   	......
   	if (handlerType != null) {
   		Class<?> userType = ClassUtils.getUserClass(handlerType);
   		// 遍历类的所有方法
   		Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
   				(MethodIntrospector.MetadataLookup<T>) method -> {
   					try {
   						// 获取方法上的映射（会读取方法上的RequestMapping注解获取url）
   						return getMappingForMethod(method, userType);
   					}
   					catch (Throwable ex) {
   						throw new IllegalStateException("Invalid mapping on handler class [" +
   								userType.getName() + "]: " + method, ex);
   					}
   				});
   		......
   		methods.forEach((method, mapping) -> {
   			Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);
   			// 将映射关系放入AbstractHandlerMethodMapping.mappingRegistry中
   			registerHandlerMethod(handler, invocableMethod, mapping);
   		});
   	}
   }
   

RequestMappingHandlerMapping解析过程

1. DispatcherServlet继承HttpServlet，所以执行链是FrameworkServlet#doGet→DispatcherServlet#doService→DispatcherServlet#doDispatch→DispatcherServlet#getHandler

   protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
   	if (this.handlerMappings != null) {
   		// handlerMappings已在onRefresh方法中初始化
   		for (HandlerMapping mapping : this.handlerMappings) {
   			// 第一个mapping就是RequestMappingHandlerMapping
   			// 获取处理程序，也就是url对应的controller和method
   			HandlerExecutionChain handler = mapping.getHandler(request);
   			if (handler != null) {
   				return handler;
   			}
   		}
   	}
   	return null;
   }
   
   // AbstractHandlerMapping#getHandler->RequestMappingHandlerMapping#getHandlerInternal->AbstractHandlerMapping#lookupHandlerMethod
   protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
   	// lookupPath就是请求路径
   	List<Match> matches = new ArrayList<>();
   	// 获取url路径匹配项
   	List<T> directPathMatches = this.mappingRegistry.getMappingsByDirectPath(lookupPath);
   	if (directPathMatches != null) {
   		// 添加映射匹配集合
   		addMatchingMappings(directPathMatches, matches, request);
   	}
   	if (matches.isEmpty()) {
   		addMatchingMappings(this.mappingRegistry.getRegistrations().keySet(), matches, request);
   	}
   	if (!matches.isEmpty()) {
   		......
   		// 至此，根据url获取到controller和method
   		return bestMatch.getHandlerMethod();
   	} else {
   		return handleNoMatch(this.mappingRegistry.getRegistrations().keySet(), lookupPath, request);
   	}
   }
   
   private void addMatchingMappings(Collection<T> mappings, List<Match> matches, HttpServletRequest request) {
   	for (T mapping : mappings) {
   		T match = getMatchingMapping(mapping, request);
   		if (match != null) {
   			// this.mappingRegistry.getRegistrations().get(mapping)就是获取HandlerMethodMapping
   			// HandlerMethodMapping保存controller和method信息的类
   			matches.add(new Match(match, this.mappingRegistry.getRegistrations().get(mapping)));
   		}
   	}
   }